Journal
APPLIED SURFACE SCIENCE
Volume 444, Issue -, Pages 387-398Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.apsusc.2018.03.078
Keywords
Acid-catalyzed hydrolysis; Characterization; Semi/full-aromatic membrane; Density functional theory calculation; Twist angle
Categories
Funding
- Korea Institute of Energy Technology Evaluation and Planning (KETEP) through human resources program in energy technology - MOTIE (the Ministry of Trade, industry & Energy, South Korea) [20164030201010]
- UNIST [1.170012.01]
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This work was systematically investigated the effects of acidic aqueous solution (15 wt% sulfuric acid as model wastewater from smelting process) on the physical and chemical properties of commercially available nanofiltration (NF) polyamide membranes, using piperazine (PIP)-based NE40/70 membranes and m-phenylene diamine (MPD)-based NE90 membrane. Surface properties of the membranes were studied before and after exposure to strong acid using various analytical tools: Scanning Electron Microscopy (SEM), Attenuated Total Reflectance-Fourier Transform Infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), contact angle analyzer, and electrophoretic light scattering spectrophotometer. The characterization and permeation results showed piperazine-based NE40/70 membranes have relatively lower acid-resistance than MPD-based NE90 membrane. Furthermore, density functional theory (DFT) calculation was also conducted to reveal the different acid-tolerances between the piperazine-based and MPD-based polyamide membranes. The easiest protonation was found to be the protonation of oxygen in piperazine-based monomer, and the N-protonation of the monomer had the lowest energy barrier in the rate determining step (RDS). The calculations were well compatible with the surface characterization results. In addition, the energy barrier in RDS is highly correlated with the twist angle (sD), which determines the delocalization of electrons between the carbonyl pCO bond and nitrogen lone pair, and the tendency of the twist angle was also maintained in longer molecules (dimer and trimer). This study clearly explained why the semi-aromatic membrane (NE40/70) is chemically less stable than the aromatic membrane (NE90) given the surface characterizations and DFT calculation results. (C) 2018 Elsevier B.V. All rights reserved.
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